Fog reduction in photographic silver halide emulsions



United States Patent "ce This invention relates to photographicmaterials and to methods of preparing them. More particularly, thisinvention relates to light-sensitive silver halide emulsions containingas a stabilizing and antifogging agent an N-substituted-3-aminomethylazolethione.

It is well known in the photographic art that light-- sensitiveemulsions, such as gelatino-silver halide emulsions, have a tendency tofog. Fog is usually caused by a prolonged ripening of the emulsion, byprolonged storage especially at elevated temperatures and humidity,

and by prolonged development. To overcome this undesirable property, ithas been the practice in this art to add certain chemical compounds tothe emulsions to. increase their stability and to reduce their tendencyto fog. However, the stabilizing and antifogging compounds heretoforeused in this art have the disadvantage that upon addition to theemulsion they cause a loss of speed and/ or contrast of the emulsion.

It is, accordindgly, an object of this invention to produce alight-sensitive emulsion which is fast, stable, has a reduced tendencyto fog and has good'contrast.

A further object of this invention resides in a lightsensitive emulsionwhich contains a compound which stabilizes the emulsion against foggingand at the same time does not materially reduce thespeed and/ or thecontrast of the emulsion.

We have discovered that N-substituted-3-aminomethylazolethiones whenadded to a light-sensitive silver halide emulsion, stabilize and inhibitthe fogging of the emulsion.

The azolethiones, the use of which is contemplated herein, may berepresented by the following formulae:

and

wherein R and R are hydrogen atoms or alkyl radicals,

e.g., methyl, ethyl, propyl, isopropyl, butyl, isobutyl,

amyl, dodecyl and the like; and acyl radical, e.g.,-acetyl, propionyland the like; a carboxyalkoxy radical, e.g., carboxymethoxy,carboxyethoxy, carboxyprop'oxy, X represents alkyl, e.g., methyl, ethyl,propyl, isopropyl, butyl, isobutyl, amyl, isoamyl, chloroethyl,carboxymethyl, allyl; aryl, .e.g., phenyl, naphthyl, tetrahydronaphthyl,aralkyl, e.g., benzyl, phenethyl; X represents hydrogen .or asubstituent having the value stated for X; and wherein X and X togetherrepresent the atoms necessary to complete a heterocyclic, hydrogenatedring system, e.g., a p'iperidine, tetrahydroquinoline, morpholine or3,081,170 Patented Mar, 12, 1963 2 piperazine ring system, Y is anoxygen, selenium or sulfur atom, and Z represents the atoms necessary tocomplete a fused-0n aromatic ring system such as a benzo or naphtho ringwhich can be further substituted.

The following specific compounds are examples of compounds belonging tothe class of compounds having the general formula given above which wehave found suitable for use as stabilizing an antifogging agents:

(llHzN CH2 GH2OH2 v 3-piperidinomethyl-benzoxazole-2rthione HzN N HzCHr-C 1 V 1, l-bisbenzoxazole-2-thione-3-methylpiperazine N HP H:

3-morpholinomethylbe DzoXazole 2-thione O 3H5 H2 v Cgl15 I3-diethy1aminomethyl-benzoxazoIe Z-thiOne .CHrCHz CH: CHg-CH23-piperidinomethyl-benzothiazole-2-thlone CHzN O CHz GZ3-morpholinomethy1-benzothlazo1e-2-thione CHzN HzN N-CH:

CHz-CH:

1,4-blsbenzothiazole-2-thione-B-methylpiperazine III OHi-OHH CHzN CH2CHr-OH: 3-piper1dinomethyl-benzoselenazole-2-thione These compounds areprepared by reacting a 2-mercapto-substituted azole of the oxazole,benzoxazole, selenazole, benz-oselenazole, thiazole and benzothiazoleseries simultaneously with formaldehyde and a primary or secondary aminein the presence of a suitable solvent such as methanol, ethanol,isopropanol and the like. The preparation of these compounds isdescribed in more detail in US. Patent 2,411,253, British patent377,253; and Journal of the Chemical Society, 1948, page 1717.

As representatives of azoles used in the reaction the following arementioned:

4-methyl-2-mercaptothiazole 4-ethyl-2-meroaptothiazole4-pnopyl-2-mercaptothiazole 4-dodecyl-2-mercaptothlazole4-buttyl-2-mercaptothi azole 4-phenyl-2-mercaptothiazole4-p-chlorophenyl-2-mereaptothiazole 4-p-methoxyphenyl-Z-mercaptothiazole4,5 -propano-2-mercaptothiazole 4,5 -dimethyl-2-mercaptothiazole 4,5-:diphenyl-2-mercaptothi-azole 4,5 -diethyl-2-mercaptothiazole5-oarbomethoxy-4-m-ethyl-Z-mercaptothiazole5-methyl-Z-mercapbobenzothiazole 6-methyl-2-mercaptobenzothiazole7-methyl-2-mercaptobenzothiazole 6-ter-t.-butyl-2-mercaptobenzothiazole61phenyl-2-mercaptobenzothiazole 5-hydroxy-Z-mercaptobenzothiazoleS-chloro-2-mercaptobenzothiazole S-bmomo-Z-mercaptob enzothiazole6-chloro 2-mercaptobenzothiazole 6-bromo-2-mercaptobenzothiazole6-nitro-2-rnercaptobenzothiazole S-amino-2-mercaptobenzothiazole6-amino-2-mercaptobenzothiazole 6-acetamido-2-mercaptobenzothiazole6-benzamido-2-mercaptobenzothiazole6-dimethylamino-2-m-ercaptobenzothiazole 5-carboxyl-2-mercaptobenzothiazole 4,6adimethyl-2-rnercaptobenzothiazole4-methyl-6-chloro-Z-mercaptobenzothiazole5,6-dichloro-2-mercaptobenzothiazole4-carboXy-6-chlono-2-mercaptobenzothiazole4,6-dimethyl-7-chloro-2-rnercaptobenzothiazole4,6-dimethyl-5,7-dichloro-3 -mercaptobenzothiazole4,5-benzo-Z-mercaptobenzothiazole 6,7-benzo-2-mercaptobenzothiazole2-mercapto-4,5,6,7-dibenzobenzothiazoleZ-mercapto-S,6-naphthobenzothiazole 2-mercapto-5,6-benzobenZothi-azole2-mercapto-4,5-fiuorenyl 1,2 -thiazole 6,7-benzo-2-mercaptobenzoselenazole 2-mercaptobenzoselenazole Z-mercaptos elenazole2-meroapto-5-methoxybenzoselenazole 2-mercapto-S-methylbenzoselenazole2-mencapto-6-methoxyquinoline 2-mercapto-6-rnethylquinoline2-mercaptobenzoxazole 2-rnercapto-51phenylbenzoxazole2-mencapto-S-methoxybenzoxazole 2-mercapto-S-methylbenzoxazole2-mercapto-4,S-benzobenzoxazole The following list is representative .ofprimary and secondary amines, the latter including cyclic amines, whichcan be condensed with formaldehyde and the mercap toazoles MethylamineEthylamine fl-Hydroxyethylamine fi-Chlo-roethylamine \Allyl-amineBenzylamine B-P-henylethylamine Ethylenediamine Ethyl amino acetatew-Aminoacetophenone Tetrahydno-fi-naphthylamine Aniline3,4-methylene-dioxybenzyl-amine ,4 Dirnethylamine DiethylamineDiethanolarnine Dipropylamine Di-n-butylamine -DiisoamylamineDibenzylamine methyldiethylethylenediamine Methylaniline Piperidine 1,2,3 ,4-tetrahydroisoquinoline 6-methoxy-1,2,3,4-tetrahydroisoquinolineMorpholine Piperiazine w-Methy-laminopnopiophenonefi-Acetylethylbenzylamine Benzyl-( 2-cyclohexanonylmethyl -amine3,4-methylenedioxybenzyl- (2acyclohexanylm ethyl -amine The antifoggingagents of our invention may be added to the emulsion at any stage duringits process of production. Thus, they may be added as a ripening finalor as a coating final. When added as a ripening final, they are addedduring the ripening or sensitivity increasing stage of the emulsionmaking process. Such addition may be made before, during or after theaddition of the soluble silver salt to the soluble halide in thepresence of a suitable colloid, such as gelatin, polyvinyl alcohol,solubilized casein or albumin. When added as a coating final, theantifogging agent of our invention is added to the emulsion just priorto coating it on a suitable support such as glass, paper, or film at atime when the emulsion has nearly attained its maximum sensitivity.

In some instances, it is advantageous to apply the antifogging andstabilizing compounds of our invention in a separate layer such as anundercoating layer or in an antiabrasion gelatin surface. Sometimes itis desirable to incorporate the compounds in one or all processing bathsor in the preand post-baths.

When used as a ripening final, the antifoggants of our invention arepreferably added to the emulsion in an amount ranging from 0.1 milligramto 20 milligrams per 0.6 mol of silver halide and when used as a coatingfinal, it is preferably added in an amount ranging from 0.5 milligram.to 50 milligrams per 0.6 mol of silver halide. The optimum amount to beadded depends primarily on the type of emulsion and should be determinedalso be used in combination with known antifoggants and stabilizers, Theantifoggants of our invention can also be used in combination withsensitiz'ers such as sulfur, metal and reduction sensitizers as well aswith speedincreasing agents and accelerators such as the reactionproducts of long-chain alcohols and ethylene oxide (see US. Patent1,970,578) and their derivatives and polyvinyl-pyrrolidone.

The novel antifoggants of our invention may be used with various'typesof photographic emulsions, such as non-sensitizedorthochromatic,panchromatic and X-ray emulsions, paper emulsions andcolor emulsions.

The following specific examples are [given as an illustration of themanner in which the anti'foggants of our invention can be used. It is tobe understood, however, that these examples are given byway ofillustration and not by way of limitation.

Example I A silver halide emulsion in gelatin containing 2 percentsilver iodide and 98 percent silver bromide was prepared in aconventional manner and brought up to its maximum light sensitivity. Itwas then readied for coating, finals were added such as sensitizing dyesand hardening agents. A 0.1 percent solution of 3-morpholinomethylbenzothiazole-Z-thione prepared according to the method described inBritish Patent 377,253 was added in varying amounts to .samples of theemulsion as an anti- -foggant and stabilizer. Each emulsion samplecontained about 0.6 mol of silver halide. The so prepared emulsionsamples were coated on a suitable cellulose ester base and dried.Samples of these film coatings were then exposed in a type IIBsensitometer and developed in a developer of the following composition:

Grains Metol 1.5 Sodiumsulfite (anhydrous) 45 Sodium bisulfite 1Hydroquinone 6 Sodium carbonate (monohydrated) .8

Water to make -1 liter.

The developed samples were short-stopped, fixed, washed and dried. Theresults obtained were as follows:

Fog at 12 Oven Fog Quantity of Compound Used Relative Minute at tiMinute Speed Develop- Development ment Example II The procedure followedwas identical to Example I, except that in place of3-morpholinomethyl-benzothiazole- Z-thione' the compound used was3-piperidinomethyl-benzoxazole-Z-thioiie prepared according to themethod described in Berichte, v01. 90, page 2246.

The procedure followed was identical to Example I, but in place of3-morpholinomethyl-benzothiazole-2- thione, the compound used was3-dimethylaminomethyl- 6' benz-oaxazole-2-thione which had been preparedaccording to the method described in Berichte, vol. 90, page 2246;

The results obtained were as follows:

Example I was repeated except that 4-chl-oro-3-morpholinomethyl-benzoxazole-2-thione was used in place of 3-morpholinomethyl-benzothiazole-Z-thione. The results obtained wereessentially the same as those reported in Example I.

The compound was prepared as follows:

A solution of 4.6 grams of 4-chloro-2mercaptobenzoxaz ole and 2.4milliliters of morpholine in 10 milliliters of methanol was cooled toabout 5 C. After the addition of 3.3 milliliters of formaldehyde (37percent) to the solution, an instantaneous reaction took place. Thereaction mixture was then left standing for 2 hours at room temperature.The product which separated was recrystallized from methanol and meltedat -151 C.

Example V Example I was repeated except that6-nitno-3-piperidinomethyl-benzothiazole-Z-thione was used in place of3- morpholinomethyl-benzothiazole-Z-thione. The results obtained werevery similar to those described in Example I.

The benzothiazolethione was prepared as follows:

A suspension of 6.3 grams of 6-nitro-2-mercaptobenzothiazole in 30milliliters 'of methanol was added to a solution of 2.5 milliliters ofpiperidine and 2.7 milliliters of formaldehyde (37 percent) in 10milliliters of methanol. The reaction mixture was left for 2 hours atroom temperature after the exothermic reaction had subsided. Theprecipitate was recrystallized from ethyl acetate and melted at 169 C.

Our invention is not limited to the detailed description containedherein, but includes all modifications that fall within the scope of theappended claims.

We claim:

1. A lightsensitive silver halide emulsion containing as an antifoggingand stabilizing agent a compound selected from the group of those havingthe'following general chemical formulae:

l CHr-A and Y 0 2:" o=s N CHz-A and /Y Y z: o s s=o :z 0 O N omoHi Nwherein X and X are selected from the group consisting of hydrogen,alkyl, aryl and aralkyl, X being a substituent other than hydrogen whenX is hydrogen, and X represents the atoms necessary to complete ahydrogenated heterocyclic ring system of the piperidine and morpholineseries.

2. A light-sensitive photographic element comprising a base and acoating of gelatino-silver halide emulsion thereon, said emulsioncontaining as an antifogging and stabilizing agent, a compound selectedfrom the group having the following formulae:

wherein R and R are selected irom the group consisting of hydrogen, analiphatic radical, an aromatic radical; Z represents the atoms necessaryto complete a fused-on aromatic ring structure, Y is a member selectedfrom the group consisting of oxygen and sulfur, A is a member selectedfrom the class consisting of and wherein X and X are selected from thegroup consisting of hydrogen, aliphatic, aryl and aralkyl radicals, Xbeing a substituent other than hydrogen when X is hydrogen, and whereinX represents the atoms necessary to complete a hydrogenated heterocyclicring system of the piperidine and morpholine series.

3. A light-sensitive structure comprising a base, a

8 layer of light-sensitive silver halide emulsion thereon, and aseparate layer adjacent said first mentioned layer containing as ananti-fogging and stabilizing agent com pound, a compound selected fromthe group having the following general chemical structures:

R-O It ("3 N Hl-A and Y z: o=s

a N 5HrA and Y Y\ 0 O z: o s s o l :2 a N OH2OH: N 5 5 H2N /N H: CH2CH2wherein R and R are selected from the group consisting of hydrogen, analiphatic radical, an aromatic radical; Z represents the atoms necessaryto complete a fused-on aromatic ring structure, Y is a member selectedfrom the group consisting of oxygen and sulfur, A is a member selectedfrom the class consisting of and wherein X and X are selected from thegroup consisting of hydrogen, aliphatic, aryl and aralkyl radicals, Xbeing a substituent other than hydrogen when X is hydrogen, wherein Xrepresents the atoms necessary to complete a hydrogenated heterocyclicring system of the piperidine and morpholine series.

4. A process of forming a photographic silver halide emulsion having areduced tendency to fog which comprises forming the emulsion, ripeningthe emulsion and during said ripening adding thereto a compound selectedfrom the group having the following general formulae:

and

. and

CH2-C a wherein R and R are selected from the group consisting orhydrogen, an aliphatic radical, an aromatic radical; Z represents theatoms necessary to complete a fused-on aromatic ring structure, Y is amember selected from the group consisting of oxygen and sulfur, A is amember selected from the class consisting of and wherein X and X; areselectedfrorn the group consisting of hydrogen, aliphatic, aryl andara-lkyl radicals, X being a substituent other than hydrogen when X ishydrogen, and wherein X represents the atoms necessary to complete ahydrogenated heterocyclic ring system of the piperidine and morpholineseries.

5. A process of forming a light-sensitive photographic element having areduced tendency to fog which cornprises forming a silver halideemulsion, ripening said emulsion, coating said emulsion on a base andadding to said emulsion just prior to the coating thereof on the base acompound selected frorn the group having the following general formulae:

wherein R and R; are selected from the group consisting 65 10 of:hydrogen, alkyl, acyl and carboxyalkexy; Z represents the atomsnecessary to complete a fused-on aromatic ring structure of the benzeneand naphthalene se- =ries; Y is a member selected from the groupconsisting of oxygen and sulfur; A is a member selected from the classconsisting of wherein X and X are selected from the group consisting ofhydrogen, alkyl, aryl and aralkyl, X being a substituent other thanhydrogen when X is hydrogen, and X represents the atoms necessary tocomplete a hydrogenated heterocyclic ring system of the piperidine andmorpholine series.

6. A light-sensitive silver halide emulsion as recited in claim 1,wherein the antifogging and stabilizing compound is3-morpholinomethyl-benzoth-iazole-2-thione.

7. A light-sensitive silver halide emulsion as recited in claim 1,wherein the antifogging and stabilizing compound is3-piperidinome-thyl-benzoxazole-2-thione.

8. A light-sensitive halide emulsion as recited in claim 1, wherein theantifogging and stabilizing compound is3-dimethylaminomethyl-benzoxazole-Z-thione.

9. A light-sensitive silver halide emulsion as recited in claim 1,wherein the antifogging and stabilizing compound is3-morpholinomethylbenzoxazole-Z-thione.

10. A light-sensitive silver halide emulsion as recited in claim 1,wherein the antifogging and stabilizing compound is3-diethylaminomethyl-benzoxazole-Z-thione.

11. A light-sensitive silver halide emulsion as recited in claim 1,wherein the antifogging and stabilizing compound is3-piperidin0methyl-benzothiazole-Z-thione.

12. A light-sensitive silver halide emulsion as recited in claim 1,wherein the antifogging and stabilizing compound is present in theemulsion in the ratio of 0.1 to milligrams per 0.6 mol of silver halide.

13. A light-sensitive silver halide emulsion as recited in claim 1,wherein the anti-fogging and stabilizing compound is present in theemulsion in the ratio of 0.1 to 20 milligrams per 0.6 mol of silverhalide.

14. A light-sensitive silver halide emulsion as recited in claim 1,wherein the antifogging and stabilizing compound is present in theemulsion in the ratio of 0.5 to 50 milligrams per 0.6 mol of silverhalide.

15. A light-sensitive silver halide emulsion as recited in claim 1,wherein said emulsion is a panchromatic emulsion.

16. A light-sensitive silver halide emulsion as recited in claim 1,containing the reaction product of a long chain alcohol and ethyleneoxide as an accelerator.

References Cited in the file of this patent UNITED STATES PATENTS2,099,374 Schwarz Nov. 16, 1937 2,463,346 Russell Nov. 9, 1948 2,819,965Murray et al. Jan. 14, 1958 2,870,015 Allen et a1. Jan. 20, 19 59 UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,081,170March 12, 1963 Emil B. Rauch et al.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 7, lines 55 and 56, column 8, lines 34 and 35, and column 9,lines 12 and 13, for "an aliphatic radical, an aromatic radical;", eachoccurrence, read alkyl, acyl and carboxyalkoxy; column 7, line 57,column 8, line 36, and column 9, line 14, for "structure,", eachoccurrence, read structure of the benzene and naphthalene series; column7, line 58, column 8, line 37, and column 9, line 15, for "sulfur,",eachoccurrence, read sulfur; column 7, line 70, column 8, line 49, andcolumn 9, line 26, for "aliphatic, aryl and aralkyl radicals,", eachoccurrence,

read alkyl, aryl and aralkyl, column 7, line 72 and column 9, line 29,strike out "wherein", each occurrence; column 8, line 51, for "wherein"read and Signed and sealed this 24th day of November 1964.

(SEAL) Attest:

ERNEST W, SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A LIGHT-SENSITIVE SILVER HALIDE EMULSION CONTAINING AS AN ANTIFOGGINGAND STABILIZING AGENT A COMPOUND SELECTED FROM THE GROUP OF THOSE HAVINGTHE FOLLOWING GENERAL CHEMICAL FORMULAE: